The ignition coil is that component of the inductive ignition system which generates the high voltage, required for the spark arc-over at the spark plug, from the low battery voltage. It is fed by the DC vehicle electrical system and supplies ignition pulses for the spark plug having the required high voltage and spark energy. This component has continued to be developed further in the course of time and has been adapted to the increased requirements on the Otto engine.
The types of ignition coil used for new developments are essentially compact ignition coils and rod-type ignition coils. In a compact ignition coil, the magnetic circuit is made up of an O core and an I core onto which the primary and secondary windings are plugged. This arrangement is built into the ignition coil housing. The primary winding, that is, the I core wound with wire, is electrically and mechanically connected to the primary plug connection. The beginning of the winding of the secondary winding is also connected, that is, the coil shell wound with wire. The connection of the secondary winding at the spark plug end is located in the housing, and the electrical contacting is produced during the mounting of the winding. Based on the compact design of the ignition coil, a construction is made possible in which the ignition coil is mounted directly on the spark plug, so that additional high-voltage connecting cables are not required. This brings about a lower capacitive load of the secondary circuit of the spark plug compared to a variant in which the mounting takes place away from the spark plug. In addition, functional safety is increased by the reduction in components, for instance, the gnawing of the ignition cable by rodents is no longer possible. The rod-type ignition coil enables the best possible utilization of space relationships in the engine compartment.
Because of the cylindrical design, the spark plug pit may also be used as a mounting space, and it makes possible a space-optimized arrangement in the cylinder head. Rod-type coils are always mounted directly on the spark plug, and therefore no additional high-voltage connecting cables are required. Rod-type ignition coils work as compact ignition coils do, according to the same inductive principle. However, because of the rotational symmetry, they are clearly different in design from compact ignition coils. The most obvious difference is in the magnetic circuit. It is made up of the same materials, the rod core that lies in the middle being made up of sheet metal lamina stamped to different widths and stacked to be approximately round and assembled to a stack. The magnetic circuit is produced via a magnetic sheet metal yoke as a rolled and slotted shell. In contrast to compact ignition coils, the primary winding, having a greater diameter, lies over the secondary winding whose coil shell accommodates the rod-type core at the same time.
Current ignition systems are predominantly free from maintenance. For diagnostic purposes, e.g. for shop maintenance, search for faults in the automobile engine, online monitoring, etc., it is expedient, however, to check orderly functioning. But, because of the direct insertion of current ignition coils into the cylinder head, an electrical diagnosis of the functioning can be carried out only with difficulty or not at all. Adapter solutions are generally eliminated, based on cramped installation positions or danger caused by high voltage. One known approach, however, represents the capacitive coupling of the high-voltage winding via a measuring probe in the form of a lamina. Together with the secondary winding, this arrangement forms a coupling capacity which makes it possible to couple out and measure a corresponding characteristic signal that corresponds to the signal curve of the generated high voltage of the ignition coil.
In the newer ignition coil designs this is partially no longer possible since, based on tightened space, the ignition coil is not accessible, or the coupling to the high-voltage winding using a measuring probe is not possible, for instance, based on a missing outer air gap of the ignition coil, or only by a design approach that requires great additional constructional effort.
It is an object of the exemplary embodiments and/or exemplary methods of the present invention to state an ignition coil which makes possible checking the functioning by capacitive coupling of the high-voltage winding, as well as a method for the capacitive coupling of the high-voltage winding of an ignition coil for diagnostic purposes.